This paper focuses on the imbalance problem of serial cells in lithium-ion batteries applied in electric vehicles (EVs). In order to meet more strict requirements of size, efficiency, cost, and reliability in commercial application, a highly-integrated and efficient distributed battery balancing system is developed. In the system, each balancing node (BN) and its controller, a designed specific integrated circuit (IC), are independent, distributed and integrated in an IC-packaged module. Besides, a 50% state-of-charge (SOC)-aligned balancing strategy is proposed and applied. The experiment and commercial application results show the designed balancing system performs excellently in improving battery capacity and extending cycle life.